Many ordnance devices, such as projectiles, mines or bombs, require a fuze to detonate the device at the desired place and time. An important part of the fuze is the safety and arming device (S/A), which contains a group of explosive components called an explosive train. The explosive train may be in an out-of-line (safe) position Or in an in-line (armed) position. When in the safe position, accidental initiation of any of the elements of the explosive train must not lead to detonation of the weapon. Conversely, when in the armed position, initiation of the explosive train must always lead to detonation of the weapon.
Prior art methods of safe arming an explosive device consist of using mechanical devices or exploding bridgewire devices. The mechanical safe arming devices physically interpose a barrier between the detonator explosive charge and the main or primary charge of the weapon. Mechanical devices have several drawbacks in that environmental degradation over an extended storage period results in a high reliability failure rate. In addition, as weapon designs become more complex, the requirements placed on mechanical safe arming devices have resulted in mechanical mechanisms which are large, expensive, complex, and thus more unreliable.
Exploding bridgewire devices remove the primary explosive charge from the detonator. The bridgewire device initiates the main charge by providing a tremendous pulse of high voltage current to the bridgewire which causes the bridgewire to explode thus directly initiating a booster charge. Because the bridgewire detonator does not contain any primary explosive, the detonator may be connected directly to the main charge without the necessity of a mechanical safing mechanism. The drawback of the exploding bridgewire detonator is that it requires a very expensive power supply to provide the necessary current for exploding the bridgewire. The power supply must be safed to the same level of protection obtained by mechanical safe arming.